docs: def clean(self, text, guess=True, format=None, **kwargs):
          """The classic: date parsing, every which way."""
          # handle date/datetime before converting to text.
          date = self._clean_datetime(text)
          if date is not None:
              return date
  
          text = stringify(text)
          if text is None:
              return
  
          if format is not None:
              # parse with a specified format
              try:
                  obj = datetime.strptime(text, format)
                  return obj.date().isoformat()
              except Exception:
                  return None
  
          if guess and not self.validate(text):
              # use dateparser to guess the format
              obj = self.fuzzy_date_parser(text)
              if obj is not None:
                  return obj.date().isoformat()
  
          return self._clean_text(text)